In the production of oil, gas and geothermal energy, drilling operations are used to create boreholes, or wells, in the earth. In recent years, lateral drilling into the targeted producing zone has become the preferred drilling procedure for extracting hydrocarbons from shale formations. In this practice, multiple engagements with the target zone are provided to allow an increased flow of production fluid into the wellbore. This is conventionally accomplished with a completion liner having interspaced packers that are hydraulically, mechanically set or swellable. Sleeve valves provided between the packers are operable with hydraulic pressure. Each sleeve valve has a circular valve seat for receivable of a ball known as a “frac ball.” Progressing down the completion liner, each sequential valve seat is smaller in opening such that the smallest valve is at the bottom of the system.
To open a sleeve valve for hydraulically fracturing a designated interval, a first, smallest frac ball, is dropped into the system for seating in the sleeve valve furthest from the surface and stopping circulation. The small frac ball will pass through the valve seat of every other sleeve valve before coming to rest on the final valve seat. In this position, the ball blocks the flow of fluid beyond the valve seat. The fluid in the production liner is then pressurized. The high pressure on the surface side of the frac ball forces the sleeve downward, exposing ports to the formation. When the lowest sleeve has been opened, the next larger frac ball is dropped to seat in the penultimate sleeve valve. This process is continued until all of the sleeve valves have been opened. When all of the reservoir sections have been treated, the well is allowed to flow back, flushing all of the frac balls back to the surface where they are captured in a ball trap.
Before this process can be initiated, it is necessary to firmly position the completion system in place in the open-hole environment. To accomplish this, a liner hanger is positioned inside the casing string, and a packer is set about the liner hanger. A cementing valve is positioned near the top of the completion system, below the liner hanger and above the packers and sleeve valves of the completion system.
A circulation blocking ball is dropped to set on a seat in a circulation valve (circulation sub) at the lowest end of the completion string. This increases the pressure inside the string and sets liner hanger slips and open hole packers. Continuation of pressure increase actuates a hydraulic valve inside the cement valve, opening the cement ports so that cement can be pumped through the tool and into the well annulus. When completed, a blocking ball or plug is sent into the tool. This allows pressure to be built-up in the tool. When the pressure is sufficient to overcome shear pin resistance, a sleeve is hydraulically repositioned to again cover the cement ports. A mill is then run into the completion string to mill out the plug or blocking ball.
It is desirable to have the ability to close the cement ports without having to trip a milling tool into the cement valve to mill the plug or blocking ball. It is further desirable to begin fracking operations without having to wait for the cement to set.
The embodiments of the present disclosure provide a unique solution to the engineering constraints and challenges of providing a cement valve that can be reclosed without the need to run a milling tool into the system to remove the blocking ball or plug, reducing the risks of problems that occur in these operations, and without the waste of time and tooling for this separate operation. It is a further advantage of the present disclosure that it is not necessary to wait for the cement to set before beginning fracking operations, thus significantly reducing the total project time of well completion.